Water -We drink it, we bathe in it, and we play in it. Water gives us life, yet too much or too little can also take life away. It's the most common substance on Earth, but far too often there's not a drop to drink. Water's extraordinary attributes give life to this planet, which might otherwise be barren and lifeless. For example, water actually expands when it freezes, becoming less dense. If ice didn't float on water, our planet would be a very different place today. Ice would sink to the bottoms of lakes and rivers, where the sun would be unable to melt it in the spring, a necessary process for making clouds and rain, which continue the flow of the cycle. This would happen every year until, eventually, there was nothing left but ice and an uninhabitable wasteland.

Water exists in three states -- solid, liquid and gas -- which comprise the Earth's hydrologic cycle, better known as the water cycle. In this cycle, fresh water comes to Earth as rain, sleet, snow and hail, pouring down over oceans and land day and night. The water that hits land runs off into larger bodies of water, like lakes and rivers, or it seeps underground and becomes groundwater, nourishing our crops in the process. When the sun comes back out, it heats up the water and makes vapor, which rises up and condenses into clouds, which gather, become heavy with water and fall back to Earth as rain.

This cycle has gone on since the world began and has made life on Earth possible. In fact, there is no more and no less water in the world today than there was when the dinosaurs were around. Think of the Earth's water cycle as the ultimate recycling method. No wonder hydrologists are so fascinated by it.

While about 70 percent of the Earth's surface is covered with water, 97 percent of the water is salty ocean water, which is unfit for human consum­ption. Of the 3 percent that's fresh water, 2 percent is frozen into glaciers, leaving only 1 percent of the entire world's water supply fit to drink.

Hydrology is the study of the flow of water through the hydrologic cycle, and Hydrologists are the people conducting the research. While most people don't think much about water, hydrologists examine every aspect of it -- where it comes from and in what quantities, where it goes, how it gets there and what happens to it in the process.

To do this, they use a lot of math and some really cool gadgets, and they even get a little wet sometimes. The results are astounding. Hydrologists help designers and engineers construct dams and levees to keep towns safe from flooding, track pollution and find new water sources they even help track water in space.

Because water is everywhere and is so critical to nearly everything we do, hydrologists span almost every branch of science, from physics and geology to astronomy and ecology.

Hydrologists don't just do things like controlling floods and water pollution. NASA has a hydrology program that maps the oceans from outer space.

While the Earth still has the same amount of water it has always had, the demand for water is greater than ever. The population keeps growing, and everyone needs to be fed and clothed with materials that have to be grown using water. The same people need to live in houses built with steel, lumber, or other various building materials -- again, these materials take a large amount of water to manufacture or grow. Of course, people also have to bathe and wash their clothes and go to the bathroom all of this  
Hydrologists are constantly looking for ways to find more water to keep up with current demands. Water treatment facilities take the water that has been used for waste and turn it back into fresh, local water that can be consumed again. Hydrologists not only look for ways to improve these facilities, they also try to find new underground wells of water and, perhaps even more importantly, figure out how to maintain these supplies with the ever-growing threat of pollution.

Pollution is industrial waste, emissions from cars, runoff of pesticides and animal wastes from farms, and extra nutrients in the soils that cause an imbalance. These can run into lakes, rivers and streams; seep into the groundwater; or collect in the air and fall back to the ground as acid rain. Mapping the course of these contaminants through environmental hydraulics is one way hydrologists help locate and clean up pollutants.